1. Field of the Invention
The invention relates to a coupling device for an electrical fixture, in particular a coupling device adapted for ceiling or wall mounted fixtures in which complementary portions of the device are quickly connectable and disconnectable, to allow the fixture to be quickly and safely connected to or disconnected from a standard outlet box.
2. Prior Art
Quickly connectable and disconnectable electrical coupling devices are known in which a female portion of the fixture is mounted in the wall or ceiling, i.e. in the building surface, and is connected to electrical power, and a complementary male portion connected to the fixture is fitted in the female portion to connect the fixture to power. Some of the devices known to the present inventor are adapted to be secured to a non-standard outlet box adjacent the wall or ceiling, and thus are not interchangeable with present fixtures. This introduces problems relating to obsolescence and inventory and in general these coupling devices have not been generally accepted, possibly for these reasons.
Other coupling devices that can be fitted to standard outlet boxes are unsatisfactory for other reasons. A typical fault is that accidental relative movement between portions of the device, for example slight rotation resulting from rotation or swinging of the fixture, can result in unintentional disconnecting of the devices which results in the fixture falling from the ceiling. Another fault is that in some coupling devices the electrical contact members themselves bear weight of the fixture. With some heavy fixtures this could result in deformation causing misalignment of the contacts so that contact is intermittent. With a relatively light fixture electrical contact between one pair or more of contacts may be lost. A further fault is that when the male portion of the coupling is removed, live contacts in the female portion are exposed to touch, thus risking electrical shock to an inexperienced person. A still further fault with some coupling devices is that, if a short circuit occurred in the fixture, the fixture could become live as no ground connection is provided. Some coupling devices are provided with ground contacts but these make contact simultaneously with the power contacts and thus an electrical shock could still result.
Most of these devices require accurate location of the outlet box relative to the building surface so that the female portion can be correctly mounted to ensure that the coupling presents a satisfactory appearance when the male portion is connected. Thus a small variation in fitting of the outlet box relatively to the building surface results in the female portion being recessed too far within the building surface, or projecting too far from the surface. If a prior art device were fitted to an inaccurately located outlet box as above, when the male portion is connected the result is unsightly. In the building trade location inaccuracies as above are to be expected because it is common practice that electrical fixtures such as outlet boxes are installed by electricians, whereas the inner walls of the building, that is the dry-wall panels or wood panelling, are installed by other trades at a later date. As the two trades work independently, it is not unusual for the positions of outlet boxes and the building surfaces to vary within a range of about one centimeter. Also it is rare for an outlet box to be mounted parallel with the building surface. In some detachable coupling devices known to the inventor there is little accommodation to the dimensional variations above and thus fitting of such devices to badly fitted outlet boxes is unsightly.